Ventilation fan



FIG. 1 is a perspective view according to our new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear front view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines illustrate portions of the ventilation fan that form no part of the claimed design. 

CLAIM The ornamental design for ventilation fan, as shown and described. 